The disclosure relates generally to phosphor compositions applicable to lighting systems. More particularly, the disclosure relates to oxynitride phosphor compositions for solid state lighting systems, and a lighting apparatus employing these phosphor compositions.
A phosphor is a luminescent material that absorbs radiation energy in a portion of the electromagnetic spectrum and emits radiation energy in another portion of the electromagnetic spectrum. Most of the phosphors emit radiation (also referred to as light herein) in the visible portion of the electromagnetic spectrum in response to excitation by a high energy electromagnetic radiation, for example ultraviolet radiation, blue radiation. Phosphors have been utilized for a variety of lighting applications such as fluorescent lamps, vacuum fluorescent displays (VFD), field emission displays (FED), plasma display panels (PDP), cathode ray tubes (CRT), light emitting diodes (LED), and the like.
However, many phosphors tend to lose efficiency gradually due to luminance deterioration. Hence, phosphors having maintained luminescence and improved lifetime performance are desired. There have been proposed nitrides and oxynitrides as phosphors that exhibit less luminance deterioration as compared to conventional phosphors. In the range of oxynitride-based phosphors, sialon (SiAlON) phosphor may be known to be superior in the fluorescent emission efficiency as well as in the temperature characteristic. In particular, europium doped α-sialon phosphor is excited in a wide wavelength region from ultraviolet rays to blue light to emits yellow to orange light and europium doped β-sialon emits green light. In addition, several phosphors may be produced by adding rare-earth elements to sialons.
Although several nitride-based and oxynitride-based phosphors have been proposed, the range of phosphors that are suitable for LEDs is limited.